Liquid reaction calorimetry

About 30 years ago, an enthalpy of formation was reported for 3,3,4,4-tetramethyl-l,2-dioxetane . Both by direct microcalorimetric combustion measurements of the neat solid and by reaction calorimetry (of the solid itself, and in acetone solution to form acetone), a consensus value was derived. Now, is the enthalpy of formation plausible , notwithstanding the very large error bars Consider reaction 6 for the dioxetane that produces 2,3-dimethyl-2,3-butanediol . The liquid phase enthalpy of reaction is —329 kJmoU. It is remarkable that this value is compatible with that for the dialkyl peroxides, ca —335 kJmoU, despite the ring strain that might be expected. 

The enthalpies of formation of the cycloalkylmagnesium bromides that have been determined by reaction calorimetry are listed in Table 3. As with other functionalized cycloalkanes and the cycloalkanes themselves, there is no regularity to these values with respect to carbon number as there are for their acyclic analogs because of the influence of ring strain on the enthalpies. Unfortunately, there are no enthalpies of formation for the bromocycloalkanes with which to compare these values there are, however, enthalpies of formation for liquid phase cycloalkanes. Figure 3 is a plot of the enthalpies of formation for the cycloalkyl-MgBr vs. those for cycloalkyl-H. There is a linear relationship with... 

Reaction calorimetry provides useful insights here even if direct enthalpy of formation measurements are absent. Liquid phase isomerization of the o- to p-tcrt-butylphenol has been shown to be exothermic hy 16.9 1.6 kJ mol [T. N. Nesterova, S. P. Verevkin, T. N. Malova and V. A. Pil shchikov, Zh. Prikl. Khim., 58, 827 (1985) Chem. Abstr., 103, 159918x (1985)] while the p- to m-isomerization in both the Uquid and gas phase is exothermic by ca 1 kJ mol [cf. V. A. Pil shchikov, T. N. Nesterova and A. M. Rozhnov, J. Appl. Chem. USSR, 54, 1765... 

FIGURE 27.2 Comparison ofconversion versus time for the reaction of Scheme 27.1 using high-performance liquid chromatography (HPLC) sampling of product concentration to in situ monitoring by Fourier transform infrared (FTIR) spectroscopy and reaction calorimetry. 

Polysulphides. The reactions of lithium and sodium with sulphur in liquid ammonia have been studied. The thermal behaviour Of the polysulphides was also investigated by means of thermogravimetric and differential thermal analyses. The enthalpies of formation of both the sulphides and polysulphides of lithium and sodium have been determined in 0.1 N-H2SO4 by reaction calorimetry. The crystal structures of two compounds, and both containing... 

Fig. 3.8 D ifference between classical liquid and supercritical reaction calorimetry.

Generally, in classical reaction calorimetry only the liquid phase is taken into account in the heat balance. This means that the gas phase in equihbrium with it is neglected because of its small contribution in terms of heat transfer and heat capacity. The situation with supercritical fluids becomes complicated as soon as they occupy all the available volume. This implies that the whole inner reactor surface has to be thermally perfectly controlled when working with supercritical fluids. In this case, the cover and the flange temperature are adjusted on-line to the reaction temperature in order to neglect the heat accumulation term. 

Bulk and apparent density Helium pycnometry Mercury porosimetry Liquid displacement Surface energy Thermal analysis tests Tempera ture-progra m med desorption and reaction Calorimetry... 

The standard molar quantities appearing in Eqs. 12.10.1 and 12.10.2 can be evaluated through a variety of experimental techniques. Reaction calorimetry can be used to evaluate AfH° for a reaction (Sec. 11.5). Calorimetric measurements of heat capacity and phase-transition enthalpies can be used to obtain the value of Sf for a solid or liquid (Sec. 6.2.1). For a gas, spectroscopic measurements can be used to evaluate S° (Sec. 6.2.2). Evaluation of a thermodynanuc equilibrium constant and its temperature derivative, for any of the kinds of equilibria discussed in this chapter (vapor pressure, solubility, chemical reaction, etc.), can provide values of ArG° and AfH° through the relations AfG° = —RTln K and ArH° = -Rd aK/d /T). 

Heat Reaction calorimetry A reaction calorimeter is designed for the investigation of reactions between liquids or solids. The calorimetric technique can be isothermal, isoperibolic or adiabatic. 

Calorimetric techniques, and liquid phase calorimetry in particular, are promising methods to study catalytic reactions [39]. Notably, the use of a differential reaction calorimeter (DRC) makes it possible to determine the most important thermodynamic data such as the heat of reaction and heat capacity of the system [40-42]. 

Various flow calorimeters are available connnercially. Flow calorimeters have been used to measure heat capacities, enthalpies of mixing of liquids, enthalpy of solution of gases in liquids and reaction enthalpies. Detailed descriptions of a variety of flow calorimeters are given in Solution Calorimetry by Grolier [17], by Albert and Archer [18], by Ott and Womiald [H], by Simonson and Mesmer [24] and by Wadso [25]. 

Film-forming chemical reactions and the chemical composition of the film formed on lithium in nonaqueous aprotic liquid electrolytes are reviewed by Dominey [7], SEI formation on carbon and graphite anodes in liquid electrolytes has been reviewed by Dahn et al. [8], In addition to the evolution of new systems, new techniques have recently been adapted to the study of the electrode surface and the chemical and physical properties of the SEI. The most important of these are X-ray photoelectron spectroscopy (XPS), SEM, X-ray diffraction (XRD), Raman spectroscopy, scanning tunneling microscopy (STM), energy-dispersive X-ray spectroscopy (EDS), FTIR, NMR, EPR, calorimetry, DSC, TGA, use of quartz-crystal microbalance (QCMB) and atomic force microscopy (AFM). 

Volume, pressure, temperature, and amounts of substances may change during a chemical reaction. When scientists make experimental measurements, however, they prefer to control as many variables as possible, to simplify the interpretation of their results. In general, it is possible to hold volume or pressure constant, but not both. In constant-volume calorimetry, the volume of the system is fixed, whereas in constant-pressure calorimetry, the pressure of the system is fixed. Constant-volume calorimetry is most often used to study reactions that involve gases, while constant-pressure calorimetry is particularly convenient for studying reactions in liquid solutions. Whichever type of calorimetry is used, temperature changes are used to calculate q. 

In solute-solvent calorimetry the compound to be studied is present as a mixture with another element or compound in solid form at room temperature and dropped into a hot calorimeter with resulting formation of a liquid product [35], In order to determine the enthalpy of formation of LaBg, Pt was added in a proportion that gave the composition of a low melting eutectic. The liquid phase formed enhanced the reaction rate and enabled the energetic parameters to be extracted [46],... 

Titration calorimetry and cylindrical internal reflection-Fourier transform infrared (CIR-FTIR) spectroscopy are two techniques which have seldom been applied to study reactions at the solid-liquid interface. In this paper, we describe these two techniques and their application to the investigation of salicylate ion adsorption in aqueous goethite (a-FeOOH) suspensions from pH 4 to 7. Evidence suggests that salicylate adsorbs on goethite by forming a chelate structure in which each salicylate ion replaces two hydroxyls attached to a single iron atom at the surface. 

This part includes a discussion of the main experimental methods that have been used to study the energetics of chemical reactions and the thermodynamic stability of compounds in the condensed phase (solid, liquid, and solution). The only exception is the reference to flame combustion calorimetry in section 7.3. Although this method was designed to measure the enthalpies of combustion of substances in the gaseous phase, it has very strong affinities with the other combustion calorimetric methods presented in the same chapter. 

Johnson et al. [143] also studied the dehydrated form of mordenite by reaction-solution calorimetry. Their results and the foregoing enthalpy of formation data lead to Af//°(Cao.289Nao.36iAlo.94oSi5.06oOi2.ooo, cr) = —5661.7 4.8 kJ mol-1. From the enthalpies of formation of both forms of mordenite and the enthalpy of formation of liquid water already quoted (—285.830 0.040 kJ mol-1), it is possible to conclude that at 298.15 K, the enthalpy of dehydration of mordenite, which corresponds to the reaction... 

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